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Name: Russell
Status: N/A
Age: 20s

Location: N/A
Country: N/A
Date: 1999 


Question:
We know that blackbody radiation produces an intensity-frequency curve that is dependent on temperature. The idea of course is that you are looking into the cavity through a hole. Why isn't the outside of the blackbody also the same color as the inside (for a given temperature)? And what it we had a blackbody made of sodium. Wouldn't there be a peak in frequencies emitted that corresponds to the traditional sodium spectrum? Is then the blackbody curve "material-specific"?


Replies:
A black body is an idealized thing -- a hypothetical object whose radiation is perfectly described by certain simple equations derived by some guys (Stefan and Boltzmann) who were thinking about how individual molecules behave without paying attention to the details of those molecules. All objects can be approximated as black bodies. For some objects in some circumstances the approximation is good enough that you don't need to describe them further; for other objects, the approximation is so bad it's useless unless combined with other approximations that idealize radiation in other ways.

A true description of an object's radiation -- one that would be correct in every detail -- would be so complicated you'd never get it all written down, so you'd never be able to use it to answer simple practical questions like "If it's red hot, will it melt aluminum?".

Tim Mooney



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